Research On Noise Reduction Characteristics Of Active And Passive Noise Control Facility For Metro Wheel-rail Noise

The main noise of metro train is wheel-rail noise.Its frequency range is composed of medium low frequency band and high frequency band.Excessive train noise will affect a large area along the metro line and interfere with people’s life and work.Excessive platform noise will reduce the comfort of station staff and passengers,and affect the speech clarity of the broadcasting system.Because the traditional sound insulation structure has a significant effect on high-frequency noise reduction and poor effect on low-frequency noise reduction,when the wheel-rail noise propagates to the sound shadow area of sound insulation structure,low-frequency sound accounts for a large proportion of the noise spectrum.The active noise control equipment can significantly reduce the low frequency sound through acoustic interference.An active and passive noise control facility was constructed,which is composed of active noise control equipment and sound insulation structure.The active noise control equipment only releases low frequency active sound waves,to reduce the low frequency component of noise in the sound shadow area of sound insulation structure,so as to improve the insertion loss of total sound pressure level(SPL).At present,there are few studies on the application of active noise reduction technology in rail transit noise reduction.The noise reduction characteristics of active and passive noise control facility was studied,on the basis of theoretical calculation,numerical simulation and field test data analysis.Based on the acoustic indirect boundary element theory,the metro train,track structure,noise barrier,ground and noise source were established to simulate the semi free field of wheel-rail noise.The simulation results are consistent with the measured data along the ground line of Beijing Metro Line 13.Based on the acoustic finite element theory,the metro train,tunnel,platform screen door,platform area and noise source were established to simulate the long space field of wheelrail noise.The simulation results are consistent with the measured data of underground platform area of Beijing Metro Line 6.Based on the dynamic theory,a vehicle-line dynamic model was established to simulate the dynamic response of the vehicle in the curved section.The regularity of vehicle lateral displacement under different speed and curve parameters was studied.Taking ensuring that each dynamic response index does not exceed the limit as the control condition,the equipment gauge of curve section corresponding to wheel rail was determined,to provide the limiting conditions for the layout of active noise control equipment in the acoustic simulation models.In the two kinds of acoustic simulation models,the active point array was arranged along the track longitudinally and equidistant.The active point array should be located in the area between the train equipment gauge and the vertical sound insulation structure.The optimal frequency band of active noise reduction,the best location of active sound source,the location of active noise reduction area,the amount of active noise reduction and the reasonable height of sound insulation structure were determined.Based on the superposition principle of radiated sound waves,a mathematical model of synthetic sound pressure at the sound receiving point was established,which was obtained by superposition of radiated sound waves from two-point noise sources and active sound waves.Through theoretical derivation,the optimal frequency band of active noise reduction,the best location of active sound source,the boundary of active noise reduction area were studied.The main conclusions are as follows:(1)The design parameters of active and passive noise control facility are determined.The horizontal distance between the active source and the track central line should be equal to the noise wavelength.The active source should have the same height as the noise source.The longitudinal distances between adjacent active sources should less than half noise wavelength.When the active sources and sound insulation structures are symmetrically arranged on both sides of the vehicle,the noise reduction effect is better than that arranged on one side.The nearest distance between the location of active source and the track central line should be 1.1m.When the distance between sound insulation structure and track central line is 3m,3.5m,4m,4.5m,5m,5.5m,6m,the height of sound insulation structure should not be respectively lower than 4.5m,4.35 m,4.2m,4.1m,3.95 m,3.85 m,3.8m.(2)The noise reduction effect of active and passive noise control facility in semi free sound field of ground section is determined.The optimal frequency band of active noise reduction is 150～320Hz.The higher the frequency,the larger the area of noise reduction area.By setting the active source,the total SPL at most receiving points in the sound shadow area can be reduced by 3～12d B,the total SPL increment at most receiving points outside the sound shadow area is less than 3d B,and the sound field in the vehicle will not be significantly affected.(3)The noise reduction effect of active and passive noise control facility in long space sound field of underground station is determined.The optimal frequency band of active noise reduction is 150～340Hz.By setting the active source,the total SPL at most receiving points in the platform area is reduced by 3～9d B.